Cisco Cisco Email Security Appliance C160 Mode D'Emploi

Consider doing the following: 

Add the relaying machine to a sender group with a mail flow policy that has unlimited messages for 
DHAP. For an explanation, see 

To facilitate tracking and troubleshooting, configure the appliance logs to show which header is 
used. See 

You will configure your appliance to use one of the following types of header to identify the original 
sender of a relayed message: 

Using custom headers is the recommended method of identifying original senders. The machine 
connecting to the original sender needs to add this custom header. The value of the header is expected 
to be the IP address of the external sending machine. For example: 

SenderIP: 7.8.9.1

X-CustomHeader: 7.8.9.1

If your local MX/MTA can receive mail from a variable number of hops, inserting a custom header is 
the only way to enable the Incoming Relays feature. For example, in 

 both path C and D lead 

to IP address 10.2.3.5; however, path C has two hops and path D has one. Because the number of hops 
can vary in this situation, you must use a custom header in order to have Incoming Relays configured 
correctly.